Since this is unrealistic code (why would you have a top-level expression without any side effects), what does it matter whether this code is optimized? Did you encounter this in a real use case?
On Sun, Oct 10, 2021 at 9:59 AM Patrick Reader <_...@pxeger.com> wrote: > Consider sequences of bytecode operations on fast locals like the > following: > > >>> def f(x): # declare as parameter so that x is a fast local > ... x > ... > >>> dis(f) > 2 0 LOAD_FAST 0 (x) > 2 POP_TOP > 4 LOAD_CONST 0 (None) > 6 RETURN_VALUE > > Given the following assumptions: > > - a LOAD_FAST cannot possibly have any side-effects outside the > interpreter stack [1] > > - a POP_TOP immediately undoes LOAD_FAST's effects on the interpreter stack > > I am wondering: why doesn't the peephole optimiser remove these opcode > constructs? > > Is it maybe because of PEP 626 - an introspection tool needs to know that > the variable is being used there? Although surely in that case the peephole > optimiser could just replace it with a single NOP? (c.f.: > https://bugs.python.org/issue42719) > > Or is one of my assumptions wrong? > > [1]: global variables are probably supposed to have the same guarantee, > but in practice this is not the case, which is why I'm focusing on the > _FAST ones; see for example > https://ato.pxeger.com/run?1=m72soLIkIz9vwYKlpSVpuhY3JyXnJBYXK_hWumQml2ikAAlNKy4FIEhJTVOIj09PLcksSc2Nj9coTs1J01HITq2EyoNAQVFmXomGUnFmSqpCalpaanKJoqKSJly6KLWktChPobi0ILVIQ1MP2TSQOVxcqRWpyRpKFUo6MPsrbA01NSEugzoQ5lAA > > _______________________________________________ > Python-Dev mailing list -- python-dev@python.org > To unsubscribe send an email to python-dev-le...@python.org > https://mail.python.org/mailman3/lists/python-dev.python.org/ > Message archived at > https://mail.python.org/archives/list/python-dev@python.org/message/767FGRV4ZL5IVBHWSAW5TJGQMGQS244Z/ > Code of Conduct: http://python.org/psf/codeofconduct/ > -- --Guido van Rossum (python.org/~guido) *Pronouns: he/him **(why is my pronoun here?)* <http://feministing.com/2015/02/03/how-using-they-as-a-singular-pronoun-can-change-the-world/>
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